The present invention relates to gas burners, and more particularly to inshot gas burners commonly used in gas furnaces, gas clothes dryers and other like gas appliances. The improved gas burner demonstrates particular advantage when utilized in recently developed high-efficiency, forced draft furnaces.
Standard atmospheric furnaces include a gas burner which is provided with a stream of pressurized combustible gas centrally into the inlet opening of the gas burner. The burner is configured with a reduced cross-section venturi which produces a relatively low pressure for aspirating primary combustion air into the burner. The air and gas then enter a slowly expanding mixing chamber. Downstream of the mixing chamber there is positioned a flame retention device having a central port therethrough and a plurality of radially outwardly extending arms defining with the burner body a plurality of circumferentially spaced flame retention ports. The heat produced by these flames rises upwardly through the furnace heat exchanger, thus inducing secondary combustion air to be drawn across the flame to cause further combustion of the gases emanating from the burner ports. This secondary combustion air flows at a relatively slow rate as it is induced into the heat exchanger merely by the force of convection.
It is also known to provide the side-by-side burners in a multi-burner furnace with radially outwardly extending carry-over ports which meet adjacent carry-over ports of adjacent burners to maintain a combustion fuel path for the ignition and re-ignition of one burner to another.
Atmospheric or convection type furnaces as described above normally exhibit a fuel efficiency rating of only about sixty-five to seventy-five percent. Due to recent concerns regarding fuel conservation, the cost of fuel and environmental pollution, manufacturers have developed new high-efficiency furnaces utilizing forced draft heat exchangers. These furnaces include heat exchangers having smaller-diameter, longer and/or more circuitous heat exchanger tubes, and can exhibit efficiency ratings of eighty to ninety percent. These high efficiency heat exchangers can no longer rely on mere convection to induce enough primary and secondary air for proper combustion. Therefore, the designers of such high-efficiency furnaces utilize blowers to induce combustion air into and through the heat exchanger tubes. Further, the designers of high-efficiency furnaces have endeavored to create the smallest possible furnace enclosure for a given furnace heat output. This has led to gas burners of shorter length than previous burners, thus (1) lessening the length of the burner air/gas mixing portion of the burner, (2) changing the burner loading, i.e., resistance to fuel flow through the burner, and (3) changing the aerodynamics of the burner to work in the increased velocity of air flow due to the combustion air blower.
The above enumerated recent changes, and others, in the furnace art have not been accompanied by sufficient gas burner improvements to provide for optimum combustion flame characteristics maintained by the gas burner.
When utilized in high-efficiency, forced draft furnaces, prior art gas burners have exhibited the following deficiencies. They may not ignite properly; they may not have the ability to hold the flame on the flame retention ports; i.e. they may exhibit flame lift off or even blow off, then re-ignite randomly creating a noise problem and contributing to improper combustion; they do not provide reliable flame carry-over performance from one burner to an adjacent burner especially when gas pressure is reduced; they may exhibit the tendency to flash back, i.e., the flame retreats to the pressurized gas source, especially when gas pressure is reduced, and they do not provide for recovery of the flame to its proper position when gas pressure is returned to normal operating pressure; they may provide improper combustion due to excess primary and/or secondary combustion air flow due to the action of the forced draft blower; they show a tendency to burn hard or lean due to excess air and improper loading, and thus produce a greater noise level and poor combustion thereby contributing to air pollution.
Generally, all of the deficiencies enumerated are compounded with the use of propane gas as opposed to natural gas.
Further, due to the wide range of furnace design parameters, such as the air flow characteristics through and surrounding the gas burner maintained by the particular forced air blower, and the size, and configuration of the heat exchanger and even the design of the furnace cabinet, the optimum burner design for one furnace model may not be the best burner design (i.e., not properly tuned), for another furnace model. This presents the problem of excessive tooling costs for producing a myriad of different burner bodies for each different furnace model. The tendency thus far in the industry is to utilize a standard burner whether or not it exhibits properly tuned results for a particular furnace model.